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<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        /* 
            null 表示“空”，“没有”
        */

        const v1 = "hello";
        const v2 = "jack";
        const v3 = null;
        
        v1 = null;//v1 所占用内存被释放
        v3 = 100;
    </script>
</body>

</html>